Interferon is a biochemical that is produced and released by animal and human cells in response to viral infection. It constitutes one of the major defense mechanisms against viral infections in mammals, including humans. In addition to its antiviral functions, research indicates that interferon has immunoregulatory properties, effects upon various cellular functions including cell division, and value as an anticancer agent.
There are at least three distinct types of human interferon. Leukocytes and other lymphoid cells produce leukocyte interferon, commonly designated as L-interferon, Le-interferon, or .alpha.-interferon. Fibroblast and other nonlymphoid cells produce fibroblast interferon, commonly designated as F-interferon or .beta.-interferon. A third category of interferon is commonly known as immune interferon, T-interferon, or .gamma.-interferon. See, e.g., Vilcek, J. et al., "Synthesis and Properties of Various Human Interferons," Microbiology-1980, Amer. Soc. for Microbiology, pp. 204-207 (1980).
F-interferon is produced and released in very minute quantitites by in vivo fibroblast cells (and, to a lesser extent, by lymphoid cells) in response to viral infections. In addition, F-interferon can be produced in vitro by cultures of fibroblast cells. Researchers have developed several methods of stimulating such cells to produce abnormally high quantities of F-interferon. See, e.g. Billiau, A. et al., "Mass production of human interferon in diploid cells stimulated by poly I:C,"Journal Gen. Virol. 19:1-8 (1973); Havell, E. A. et al., "Production of high-titered interferon in cultures of human diploid cells," Antimicrob. Ag. Chemother. 2:476-484 (1972); Ho, M. et al., "Accentuation of production of human interferon by metabolic inhibitors," Proc. Soc. Exp. Biol. Med. 139:259-262 (1972). However, some problems still inhibit the effective use of F-interferon in biomedical research and treatment.
One important characteristic that decreases the usefulness of F-interferon is its hydrophobicity. In general, a hydrophobic substance within an aqueous or biological solution will tend to adopt configurations that minimize the area of contact between the substance and the solution. Hydrophobic substances in aqueous or biological solutions tend to form globules, and to cling to substrates such as filters and cell walls. This reduces the ability of the substance to be absorbed by and transported within an animal or human body or tissue culture.
As normally produced by fibroblast cells in vitro, F-interferon tends to become attached to and surrounded by carbohydrate groups and possibly other types of non-polar hydrophobic moieties. Such carbohydrate moieties may be natural and indigenous constituents of interferon molecules, rather than merely impurities and contaminants. However, research performed to date indicates that F-interferon retains some or all of its beneficial properties and effectiveness if carbohydrate moieties are removed from the remaining interferon molecule.
Early research indicated that injections of sizable quantities of fibroblast interferon produce very small quantities of F-interferon in the blood serum of animals and humans. See Billiau, A. et al., "Human Fibroblast Interferon for Clinical Trials: Pharmacokinetics and Tolerability in Experimental Animals and Human," Antimicrob. Ag. Chemother. 16:56-63 (1979); Edy, V. G. et al, "Non-appearance of Injected Fibroblast Interferon in Circulation," Lancet 1:451-452 (1978). Clearance of F-interferon from the bloodstream of an injected animal or human may be partially responsible for small quantities of F-interferon being detected in the bloodstream after injection. See Cantell, K. et al., "Pharmacokinetics of Human Leukocyte Interferon," J. Inf. Dis. 133:A6-A12 (1976). Inactivation by animal or human blood also may be partially responsible for small quantities of F-interferon being detected in the bloodstream after injection. See Cesario, T. C. et al., "Inactivation of Human Interferon by Body Fluids," Tex. Rep. Biol. Med. 35:443-448 (1977). However, research indicates that clearance and inactivation probably are not the primary reasons why fibroblast interferon is poorly absorbed into the bloodstream after intramuscular injection. See Vilcek, J. et al., "Pharmacokinetic Properties of Human Fibroblast and Leukocyte Interferon in Rabbits," Journal of Clinical Microbiology 11:102-105 (1980). This research implies that the problem of low postinjection serum activity is caused primarily by the tendency of fibroblast interferon to cling to tissue at the site of injection, which in turn appears to be caused by the hydrophobicity of fibroblast interferon.
Carbohydrate and other hydrophobic moieties also cause or exacerbate various other problems in producing, storing, and using fibroblast interferon, in addition to the problem of low serum activity after injection. For example, numerous types of molecules and enzymes react with carbohydrates to form various by-products. Therefore, carbohydrate moieties may tend to reduce the stability and longevity of fibroblast interferon, both in vivo and in vitro during its production, storage, and use.
In addition, hydrophobic impurities and contaminants within an aqueous or biological solution containing fibroblast interferon will tend to mix with and adhere to the interferon, rendering it impure and interfering with its desirable properties. Adverse reactions, including fever and nausea, by patients injected with impure interferon have already been noted by researchers. See, e.g., Billiau, A. et al., "Human Fibroblast Interferon for Clinical Trials: Pharmacokinetics and Tolerability in Experimental Animals and Humans," Antimicrob. Agents and Chemotherapy 16:46-63 (1979).
Other problems caused by the relative reactivity of moieties on interferon are likely to become apparent during research and medical usage involving interferon. Any such problems are likely to be alleviated or eliminated by treatment of the interferon to remove or modify such moieties.